docs: Add release note change for zcbor version

Adds a release note file indicating that zcbor files have been
updated to version 0.7.0

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
diff --git a/docs/release-notes.d/zcbor-update.md b/docs/release-notes.d/zcbor-update.md
new file mode 100644
index 0000000..ec6c790
--- /dev/null
+++ b/docs/release-notes.d/zcbor-update.md
@@ -0,0 +1 @@
+- zcbor library files have been updated to version 0.7.0